Device and method of reducing bias flow in oscillatory ventilators

ABSTRACT

A device and method of ventilating a patient reduces the bias flow relative to existing oscillatory ventilators. The device has a gas flow circuit comprising an oscillating line, a patient line and an exhalation or a return line. A gas supply line is and an outlet valve are in pneumatic communication with the gas flow circuit. One or more CO 2  scrubbers and one or more check valves are provided in the circuit. A method of ventilating using such a device is also disclosed.

[0001] This application claims priority to U.S. provisional patentapplication No. 60/353,461 filed on Feb. 1, 2002 and is also acontinuation in part of U.S. patent application Ser. No. 09/631,464filed on Aug. 3, 2000 which in turn claims priority to U.S. provisionalapplication No. 60/146,863, filed on Aug. 3, 1999, the disclosures ofwhich are incorporated herein by reference.

FILED OF THE INVENTION

[0002] The present invention relates generally to ventilators forsupporting breathing in animals. More particularly, the presentinvention provides a device and method of ventilating.

DISCUSSION OF RELATED ARTS

[0003] There are many situations in which normal breathing by an animalpatient is impaired and must be assisted by external means. Oscillatoryventilators are used to facilitate breathing in such situations. Amongthe types of ventilators available are high frequency oscillatingventilators. U.S. Pat. No. 4,719,910 describes a high frequencyoscillating ventilator. A flow of gas is conducted from a gas source toa high frequency oscillator. The high frequency oscillator comprises ahousing including a magnet and having a diaphragmatically sealed pistonmounted therein, an inlet connecting the space within the housing on thefirst side of the diaphragm to the gas conducting means, and a coilmounted to the first side of the diaphragm. Circuitry is provided whichis operable to reverse the polarity of the flow of the current in thecoil, thereby causing the diaphragm to move back and forth within thehousing. A tube connecting the space on the second side of the diaphragmto the gas source and the patient's airway is provided.

[0004] In the prior art, inspiratory gas is moved into and out of thepatient via a U-shaped tube and movement of the diaphragm. For purposesof describing the prior art, the U-shaped tube can be described ashaving a first limb with a distal end, a second limb with a distal end,and a tube between the limbs. Connected to the tube between the limbs isanother tube (the “patient line”) that delivers gas from the U-shapedtube to the patient and also delivers gas from the patient to theU-shaped tube. The patient line may be connected to the patient via anendotracheal tube. The distal end of the first limb is placed in sealingrelation to the diaphragm so that gas inside the U-shaped tube is causedto oscillate as the diaphragm moves back and forth. Gas suitable forinspiration (“inspiratory gas”) is supplied at a location on theU-shaped tube between the diaphragm and the patient line.

[0005] Inspiratory gas passes through the first limb of the U-shapedtube, and exhaled gas exits to the atmosphere through the second limb ofthe U-shaped tube and out of the distal end of the second limb. Toprevent expired gases from being drawn back into the first limb duringthe expiratory phase of breathing, more inspiratory gas than needed bythe patient is provided in order to move the expired gas into the secondlimb. The inspiratory gas provided in excess of the needs of the patientis referred to herein as “bias flow”.

[0006] To move expired gas into the second limb of the U-shaped tube, aninspiratory gas flow rate of approximately 20 liters per minute is usedwhen ventilating infants, and as much as 60 to 80 liters per minute whenventilating older children and adults. Such large volumes of inspiratorygas would quickly exhaust the available supply of most transport andambulance vehicles. Furthermore, such prior art devices necessitatelarge and costly volumes of therapeutic gases that might be mingled withthe inspiratory gas (e.g., volatile anesthetics, nitric oxide, vaporizedperfluorocarbons, helium/oxygen mixtures etc.). Finally, such prior artdevices are inefficient when one considers the amount of inspiratory gasrequired by the patient and the relatively large amount of inspiratorygas supplied to the ventilator.

SUMMARY OF THE INVENTION

[0007] An object of the present invention is to provide a device and amethod of ventilating. The object is achieved by a ventilating devicehaving an oscillator, such as an oscillatory diaphragm, and gas flowcircuit comprising an oscillating line having a first end in sealing orpneumatic relationship with the oscillator. A gas supply line isconnected to the oscillating line, and a patient line is connected to asecond end of the oscillating line. An outlet line is in pneumaticcommunication with the patient line, and an end of the outlet linedistal from the patient line is connected to an outlet valve. The outletvalve releases gas from the outlet line during inhalation, and preventsthe release of gas from the outlet line during exhalation. In oneembodiment of the invention, the device has an oscillating line with agas supply line connected thereto, a patient line connected to thesecond end of the oscillating line, an outlet line in pneumaticcommunication with the patient line, an outlet valve connected to theoutlet line, one or more CO₂ scrubbers and one or more check valves toensure unidirectional flow of gas through the one or more scrubbers.This device of this embodiment can be attached to an oscillatingventilator.

[0008] In another embodiment, the device of the present invention isadapted for connecting to the U-type ventilator attachments of the priorart. In one embodiment of the invention, the device has a gas flowcircuit comprising an oscillating line having a first end and a secondend. The first end is adapted for connecting to an oscillatingventilator either directly or through another device such as aconventional U-type tube, a patient line connected to the second end ofthe oscillating line, a return line connected to the oscillating line,one or more CO₂ scrubbers and one or more check valves to ensureunidirectional flow of gas. Optionally, the device may have an outletvalve and a gas supply line or when used in conjunction with aconventional U-type tube, may use the outlet valve and the gas supplyline of the conventional U-type tube.

[0009] In a method according to the present invention, a ventilationdevice, such as the one described above, is provided. A patient inpneumatic communication with the patient line is provided and gas issupplied to the oscillating line. The oscillator is moved toward theoscillating line and the outlet valve is opened. Then, the oscillator ismoved away from the oscillating line and the outlet valve is closed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] For a fuller understanding of the nature and objects of theinvention, reference should be made to the following description takenin conjunction with the accompanying drawings, in which:

[0011]FIG. 1 is a schematic sectional view of a device according to thepresent invention illustrating the major components of the device andutilizing a CO₂ scrubber.

[0012]FIGS. 2a and 2 b are schematic sectional representations of theclosed and open positions respectively of an outlet valve according tothe present invention.

[0013]FIGS. 3a and 3 c are each a schematic sectional representation ofan embodiment of the present invention.

[0014]FIG. 3b is a schematic sectional representation of anotherembodiment of the present invention.

[0015]FIGS. 4a and 4 b are schematic sectional views of otherembodiments of the present invention having a CO₂ scrubber.

[0016]FIG. 5 is a schematic sectional representation of anotherembodiment of the present invention.

[0017]FIG. 6 is a schematic sectional view of another embodiment of theinvention without a CO₂ scrubber.

[0018]FIGS. 7a and 7 b are schematic sectional representations of theclosed and open positions respectively of another outlet valve accordingto the present invention.

[0019]FIG. 8 is a flow chart showing steps of a method according to thepresent invention.

[0020]FIGS. 9a, 9 b, 9 c and 9 d are schematic sectional views of anembodiment of the invention that can be connected to a U-type oscillatortube (9 a, 9 b and 9 c) or to an oscillating ventilator (9 d).

DETAILED DESCRIPTION OF THE INVENTION

[0021] As used herein the term “gas” means a pure gas or a mixture ofgases. Thus, the term “gas” may refer to a mixture of O₂ and N₂, and mayinclude therapeutic gases.

[0022] A device 10 according to the present invention can be connectedto an oscillating machine having an oscillator 11, such as a diaphragm,like those described in U.S. Pat. No.4,719,910 and U.S. Pat. No.5,307,794. As illustrated in FIG. 1, an inspiratory gas source 5 isconnected to a device 10 according to the present invention throughsupply line 8. The flow of inspiratory gas into the device 10 can beregulated by a flow regulator 9 connected to supply line 8. Preferably,the flow of inspiratory gas from supply line 8 and into connecting line18 is essentially at a constant rate. Connecting line 18 is connected tothe oscillating line 14.

[0023] In the embodiment shown in FIG. 1, an inbound check valve 20 isin the oscillating line 14. The portion of the oscillating line 14 thatis downstream of the inbound check valve 20 is referred to herein as theinbound line 15. The check valve 20 permits the flow of gas in thedirection of arrow 21 and prevents the flow of gas in the oppositedirection. When the pressure on the upstream side of the inbound checkvalve 20 is higher than the pressure on the downstream side of theinbound check valve 20, the inbound check valve 20 opens allowing gas toflow in the direction of arrow 21. When the pressure on the upstreamside of the inbound check valve 20 is lower than on the downstream side,the inbound check valve 20 shuts, effectively stopping the flow of gasthrough inbound line 15.

[0024] Further downstream of inbound check valve 20, for example alonginbound line 15 may be placed an O₂ sensor 24 and a CO₂ sensor 22 tomonitor the quality of the gas therein. Additional modifiers andmonitors like humidifiers, nebulizers and the like can also beinstalled. Inbound line 15 connects to patient line 25, which is in turnconnected to an endotracheal tube (not shown in FIG. 1) for delivery ofgas to the patient's airways, and ultimately to the patient's lungs.

[0025] Inbound line 15 is also connected to exhalation line 30. Inexhalation line 30 may be placed a pressure monitoring device, such as amanometer, through port 28. Exhalation line 30 includes a scrubber line36 and connects to recirculation line 34. Recirculation line 34 connectsto the oscillating line 14. At the junction of recirculation line 34 andscrubber line 36 is a two-position valve 32 which directs the flow ofgas either toward the recirculation line 34 or toward the scrubber line36. The two position valve 32 is normally positioned to direct the flowof gas to the scrubber line 36. Preferably, the two-position valve 32 isnormally adjusted so that no gas flows through recirculation line 34.

[0026] Included in the exhalation line 30 is a scrubber canister 38, anoutbound line 40, and a discharge line 16. A second scrubber 68 may alsobe included and used when the scrubber canister 38 is not being used,for example, while scrubber canister 38 is being replaced or recharged,for example, by purging CO₂ using a separate flow of gas (not shown).The scrubber valves 70A and 70B preferably operate together so thateither scrubber canister 38 or the second scrubber 68 is in operation.In a preferred embodiment, the scrubber valves 70A and 70B are not twoseparate valves, but instead a slide type valve, commonly used in themedical community, having an outer cylindrical shell and a movable innercylinder, each with holes therethrough that allow either the scrubbercanister 38 or the second scrubber 68 to be in service.

[0027] The outbound line 40 is fitted with an outbound check valve 42,which permits the flow of gas in the direction of arrow 43 and preventsthe flow of gas in the opposite direction. Downstream of the outboundcheck valve 42 is discharge line 16 having within it a shut-off valve44. The shut-off valve 44 is normally set to the open position. Theshut-off valve 44 in its open position, permits the flow of gas, but inits closed position blocks the flow of gas. Discharge line 16 connectsto oscillating line 14.

[0028] Oscillating line 14 connects at one end to the patient line 25,and is placed in sealing relationship at the other end with theoscillator 11. Preferably, the oscillator 11 is a diaphragm of a highfrequency oscillating machine. Connected to the oscillating line 14 isan outlet line 50, which is in turn connected to outlet valve 52. Theoutlet valve 52 may open and shut in response to a control pressureprovided via control line 54. The closed and open positions of outletvalve 52 are shown in FIGS. 2a and 2 b respectively. The externalcontrol pressure may be provided to control line 54 by the oscillatingmachine that controls the oscillator 11. In one embodiment of thepresent invention, the control pressure provided by line 54 issubstantially stable and the oscillating pressure in line 14 caused bymovement of the diaphragm 11 causes the outlet valve 52 to open andclose. Alternatively, operation of the outlet valve 52 may be by othermeans, such as a solenoid.

[0029] High frequency oscillation of the oscillator 11 facilitatesmovement of gas into and out of the patient's airways. Thus, during theinspiration phase, when the oscillator 11 is moving toward theoscillating line 14, a pressurizing cycle occurs, and during theexpiration phase, when the oscillator 11 is moving away from theoscillating line 14, a depressurizing cycle occurs. During thepressurizing cycle, the pressure on the upstream side of the inboundcheck valve 20 increases, forcing it to open thereby allowing gas toflow in the direction of arrow 21, and consequently into the patient'slungs via patient line 25. At the same time, due to the oscillator 11moving toward the device 10, the pressure on the downstream side ofoutbound check valve 42 becomes higher than the pressure on its upstreamside, which forces the outbound check valve 42 to close, therebypreventing the flow of gas from discharge line 16 into the scrubbercanister 38.

[0030] During the expiration phase (or depressurizing part of thecycle), the oscillator 11 moves away from the oscillating line 14 andthe pressure differential across the inbound check valve 20 causes theinbound check valve 20 to close. The exhaled gas is pushed by thepatient's lungs into exhalation line 30, and into the CO₂ scrubbercanister 38. At the same time, the pressure differential across theoutbound check valve 42 causes the outbound check valve 42 to open.Thus, CO₂ scrubbed gas is returned to oscillating line 14 through thenormally open shut-off valve 44. The gas returning to the oscillatingline 14 via the discharge line 16 mixes with the gas in the oscillatingline 14. The gas in oscillating line 14 is moved toward the cutlet valve52 when the inbound check valve 20 is closed by the movement of theoscillator 11. FIGS. 2a and 2 b illustrate the open and closed positionsof the pneumatic version of the outlet valve 52. When the controlpressure supplied by control line 54 exceeds the pressure in theoscillating line 14 (FIG. 2a ), the outlet valve 52 is in the closedposition and gas from oscillating line 14 is prevented from escapingfrom the device 10. When the control pressure supplied by control line54 is less than the pressure in the oscillating line 14 (FIG. 2b), theoutlet valve 52 is in the open position and gas from oscillating line 14is allowed to escape from the device 10. In the embodiments shown inFIGS. 1 through 5, preferably the outlet valve 52 is closed for at leastpart of the expiration phase (i.e. when the pressure in oscillating line14 is decreasing due to movement of the oscillator 11 away from thedevice 10), and the outlet valve 52 is open for at least part of theinspiration phase (i.e. when the pressure in oscillating line 14 isincreasing due to movement of the oscillator 11 toward the device 10).

[0031] The CO₂ scrubber canister 38 in the device 10 of the presentinvention may be used in other locations. For example, as shown in FIGS.3a, 3 b and 3 c, the scrubber canister 38 may be placed at the end ofpatient line 25 distal from the inbound line 15. As shown in FIGS. 3aand 3 c, suitable check valves 20, 42 and return line 67 can beincorporated to assure unidirectional flow through the scrubber canister38. A bypass line 66 could be provided to accommodate replacement of thescrubber canister 38. In a preferred embodiment of the presentinvention, the second scrubber canister 68 is provided in the bypassline 66. The second scrubber canister 68 may be incorporated into anyembodiment described herein which has a scrubber canister 38. The devicedepicted in FIGS. 3a, 3 b and 3 c could be used with prior artventilator circuits.

[0032] The scrubber canister 38 contains a material that removesunwanted gas, such as CO₂. For example, the scrubber canister 38 maycontain sodium hydroxide, calcium hydroxide, or barium hydroxide. Sodiumhydroxide and calcium hydroxide mixed with silica is available as SodaLime™. Another commercially available CO₂ scrubber is Baralyme™ whichcomprises barium hydroxide and calcium hydroxide. Once the CO₂ scrubbercanister 38 is depleted of its scrubbing capacity, it can be replaced.To replace the scrubber canister 38, the two-position valve 32 is set todirect the gas from the exhalation line 30 to the recirculation line 34,while the shut-off valve 44 is set to the closed position. Uponreplacement of the scrubber canister 38, the two-position valve 32 andthe shut-off valve 44 are reset to their normal positions.

[0033]FIGS. 4a and 4 b show two additional embodiments of the presentinvention. As illustrated in FIG. 4a, the scrubber canister 38 may beplaced in the oscillating line 14 upstream of the CO₂ and O₂ sensors 22,24, or as shown in FIG. 4b, downstream of the sensors 22, 24. In theembodiments shown in FIGS. 4a and 4 b, check valves are not required todirect the flow of inspiratory gas toward the patient line 25 or todirect the flow of expired gas toward the scrubber canister 38.Normally, gas moves in both directions through the scrubber canister 38.To replace the scrubber canister 38, two block valves 62, 64 can betemporarily adjusted so that gas flows through the bypass line 66.

[0034]FIG. 5 shows another embodiment of the present invention in whichthe scrubber is located in the oscillating line 14, and gas flowsthrough the scrubber canister 38 toward the patient line 25. Flow fromthe patient line 25 moves through the exhalation line 30 to oscillatingline 14. A check valve 42 is in bypass line 66 to assure that flow movesthrough exhalation line 30 in one direction only. An additional checkvalve 20 may be included in oscillating line 14 to assure flow throughthe scrubber canister 38 in one direction only.

[0035] In another embodiment of the present invention, illustrated inFIG. 6, instead of scrubbing CO₂ from the exhaled gas, the exhaled gasis simply allowed to leave a device 100. The device 100 is connected toan inspiratory gas source 5 through connecting line 18. The inspiratorygas enters an oscillating line 14 and moves toward the patient line 25in the direction of arrow 21 via the inbound check valve 20. CO₂ and O₂sensors 22, 24 and pressure monitoring port 28 can be placed near thepatient line 25. The exhaled gas is conducted by the exhalation line 30to another type of outlet valve 52. The outlet valve 52 shown in FIGS.6, 7a and 7 b operates based on the pressure differential betweenoscillating line 14 and the exhalation line 30. During the pressurizingcycle, outlet valve 52 is caused to close the end 132 of exhalation line30 by the rising pressure in oscillating line 14. However, during thedepressurizirig phase, the pressure in the outlet line 50 causes theoutlet valve 52 to open the end 132 and allow gas to escape to theatmosphere. Preferably, for at least part of the pressurization cycle,outlet valve 52 is closed and there is no communication between theexhalation line 30 and the atmosphere, and for at least part of thedepressurization cycle, outlet valve 52 is open and there iscommunication between line 30 and the atmosphere.

[0036]FIGS. 7a and 7 b show a preferred embodiment of the outlet valve52 shown in FIG. 6. The outlet valve 52 in FIGS. 7a and 7 b has a firstflexible membrane 300 disposed in the oscillating line 14 and a secondflexible membrane 303 situated to selectively close the end 132 of theoutlet line 50. The flexible membranes 300, 303 are connected by apressure communication line 306. The pressure communication line 306 maybe filled with a gas or a fluid. When the pressure in the pressurecommunication line 306 is above the pressure in outlet line 50, the end132 of the outlet line 50 is closed by the second flexible membrane 303.When the pressure in the outlet line 50 is above the pressure in thepressure communication line 306, gas is allowed to escape from the end132 of the outlet line 50. It will be recognized that due to the firstflexible membrane 300, the pressure in oscillating line 14 will changethe pressure in the pressure communication line 306.

[0037] In a preferred embodiment, a control pressure line 309 isconnected to the pressure communication line 306. When the controlpressure line 309 is provided, the pressure in the pressurecommunication line 306 may be changed, and thereby, the pressure in theoutlet line 50 required to open the end 132 of the outlet line 50 may bechanged.

[0038] In another embodiment of the invention shown in FIGS. 9a, 9 b and9 c, device 10 may be connected to an U-type oscillator tube (termedherein as a connecting tube) of the prior art. The U-type tubestypically have a gas supply line and an outlet valve or means. In thisembodiment, the device has a gas flow circuit comprising an oscillatingline, a patient line and a return line. The first end of the oscillatingline 14 is adapted for communication with a connector 402 of the U-typeoscillator tube 400 as indicated by dotted lines 404. The second end ofthe oscillating line 14 is connected to patient line 25. A return line67 is provided for return of exhaled air. The return line at both endsis connected to the oscillating line. On the oscillating line betweenthe ends of the return line is located check valve 20 to move the gastoward patient line 25. A CO₂ scrubber 38 is located in the return line(FIG. 9a) or in the oscillating line (FIG. 9b). In a preferredembodiment (FIG. 9a), another check valve 42 is provided in the returnline. The device may also have a gas supply line and an outlet valve.For use of this device directly with an oscillating ventilator 410 asindicated by dotted lines 404 (FIG. 9d), a gas supply line 8 having aflow regulator 9 is connected to any location in the gas flow circuitthrough connecting line 18. An outlet valve 52 may also be placed at anylocation in the gas flow circuit. One example of a location for thesupply line 18 and outlet valve 52 is shown in FIG. 9d. The scrubbercanister 38 may be placed at any location in the oscillating line orreturn line, but is preferably placed in the return line. Optionally, asshown in FIG. 9c, a second CO₂ scrubber canister 68 may be provided inanother return line 66. Scrubber valves 70A and 70B operate as describedabove such that either scrubber canister 38 or scrubber canister 68 isin use. Oxygen and CO₂ sensors, and pressure monitoring devices can alsobe placed in the gas flow circuit as shown in FIGS. 1, 4a, 4 b or 6.

[0039] To illustrate the concept of the present invention, mathematicalrelationships were developed for the device 10 shown in FIG. 1. Tables1-10 below list data corresponding to these mathematical relationships.In the tables:

[0040] VO₂ is the volume rate of oxygen consumed by the patient;

[0041] VI is the volume rate of inspiratory gas supplied to the device10;

[0042] FiO₂ is the mole fraction of oxygen in the inspiratory gas;

[0043] FmO₂ is the mole fraction of oxygen in the mixed gas crossinginbound check valve 20;

[0044] FiO₂=1-FiN₂. where FiN₂ is the mole fraction of nitrogen in theinspiratory gas;

[0045] FmO₂=1-FmN₂, where FmN₂ is the mole fraction of nitrogen in themixed gas exiting the outlet valve 52;

[0046] VI=K+VO₂, where K=outflow volume from outlet valve;

[0047] VI×FiN₂=K×FmN₂;

[0048] VI (1-FiO₂)=K (1-FmO₂);

[0049] (VI÷K) (1-FiO₂=1-FmO₂;

[0050] FmO₂=1−((VI÷K) (1-FiO₂)). TABLE 1 VO₂ VI K ml/kg/ ml/kg/ FmO₂ ÷ml/kg/ min min FiO₂ FmO₂ FiO₂ min Vi ÷ VO₂ 5.0 6.0 0.21 −3.74 −17.81 1.01.2 5.0 10.0 0.21 −0.58 −2.76 5.0 2.0 5.0 20.0 0.21 −0.05 −0.25 15.0 4.05.0 30.0 0.21 0.05 0.25 25.0 6.0 5.0 40.0 0.21 0.10 0.46 35.0 8.0 5.050.0 0.21 0.12 0.58 45.0 10.0 5.0 60.0 0.21 0.14 0.66 55.0 12.0 5.0 70.00.21 0.15 0.71 65.0 14.0 5.0 80.0 0.21 0.16 0.75 75.0 16.0 5.0 90.0 0.210.16 0.78 85.0 18.0 5.0 100.0 0.21 0.17 0.80 95.0 20.0 5.0 200.0 0.210.19 0.90 195.0 40.0* 5.0 500.0 0.21 0.20 0.96 495.0 100.0 5.0 1000.00.21 0.21 0.98 995.0 200.0

[0051] TABLE 2 VO₂ VI K ml/kg/ ml/kg/ FmO₂ ÷ ml/kg/ min min FiO₂ FmO₂FiO₂ min Vi ÷ VO₂ 5.0 6.0 0.30 −3.20 −10.67 1.0 1.2 5.0 10.0 0.30 −0.40−1.33 5.0 2.0 5.0 20.0 0.30 0.07 0.22 15.0 4.0 5.0 30.0 0.30 0.16 0.5325.0 6.0 5.0 40.0 0.30 0.20 0.67 35.0 8.0 5.0 50.0 0.30 0.22 0.74 45.010.0 5.0 60.0 0.30 0.24 0.79 55.0 12.0 5.0 70.0 0.30 0.25 0.82 65.0 14.05.0 80.0 0.30 0.25 0.84 75.0 16.0 5.0 90.0 0.30 0.26 0.86 85.0 18.0 5.0100.0 0.30 0.26 0.88 95.0 20.0 5.0 200.0 0.30 0.28 0.94 195.0 40.0* 5.0500.0 0.30 0.29 0.98 495.0 100.0 5.0 1000.0 0.30 0.30 0.99 995.0 200.0

[0052] TABLE 3 VO₂ VI K ml/kg/ ml/kg/ FmO₂ ÷ ml/kg/ min min FiO₂ FmO₂FiO₂ min Vi ÷ VO₂ 5.0 6.0 0.40 −2.60 −6.50 1.0 1.2 5.0 10.0 0.40 −0.20−0.50 5.0 2.0 5.0 20.0 0.40 0.20 0.50 15.0 4.0 5.0 30.0 0.40 0.28 0.7025.0 6.0 5.0 40.0 0.40 0.31 0.79 35.0 8.0 5.0 50.0 0.40 0.33 0.83 45.010.0 5.0 60.0 0.40 0.35 0.86 55.0 12.0 5.0 70.0 0.40 0.35 0.88 65.0 14.05.0 80.0 0.40 0.36 0.90 75.0 16.0* 5.0 90.0 0.40 0.36 0.91 85.0 18.0 5.0100.0 0.40 0.37 0.92 95.0 20.0 5.0 200.0 0.40 0.38 0.96 195.0 40.0 5.0500.0 0.40 0.39 0.98 495.0 100.0 5.0 1000.0 0.40 0.40 0.99 995.0 200.0

[0053] TABLE 4 VO₂ VI K ml/kg/ ml/kg/ FmO₂ ÷ ml/kg/ min min FiO₂ FmO₂FiO₂ min Vi ÷ VO₂ 5.0 6.0 0.50 −2.00 −4.00 1.0 1.2 5.0 10.0 0.50 0.000.00 5.0 2.0 5.0 20.0 0.50 0.33 0.67 15.0 4.0 5.0 30.0 0.50 0.40 0.8025.0 6.0 5.0 40.0 0.50 0.43 0.86 35.0 8.0 5.0 50.0 0.50 0.44 0.89 45.010.0 5.0 60.0 0.50 0.45 0.91 55.0 12.0* 5.0 70.0 0.50 0.46 0.92 65.014.0 5.0 80.0 0.50 0.47 0.93 75.0 16.0 5.0 90.0 0.50 0.47 0.94 85.0 18.05.0 100.0 0.50 0.47 0.95 95.0 20.0 5.0 200.0 0.50 0.49 0.97 195.0 40.05.0 500.0 0.50 0.49 0.99 495.0 100.0 5.0 1000.0 0.50 0.50 0.99 995.0200.0

[0054] TABLE 5 VO₂ VI K ml/kg/ ml/kg/ FmO₂ ÷ ml/kg/ min min FiO₂ FmO₂FiO₂ min Vi ÷ VO₂ 5.0 6.0 0.60 −1.40 −2.33 1.0 1.2 5.0 10.0 0.60 0.200.33 5.0 2.0 5.0 20.0 0.60 0.47 0.78 15.0 4.0 5.0 30.0 0.60 0.52 0.8725.0 6.0 5.0 40.0 0.60 0.54 0.90 35.0 8.0* 5.0 50.0 0.60 0.56 0.93 45.010.0 5.0 60.0 0.60 0.56 0.94 55.0 12.0 5.0 70.0 0.60 0.57 0.95 65.0 14.05.0 80.0 0.60 0.57 0.96 75.0 16.0 5.0 90.0 0.60 0.58 0.96 85.0 18.0 5.0100.0 0.60 0.58 0.96 95.0 20.0 5.0 200.0 0.60 0.59 0.98 195.0 40.0 5.0500.0 0.60 0.60 0.99 495.0 100.0 5.0 1000.0 0.60 0.60 1.00 995.0 200.0

[0055] TABLE 6 VO₂ VI K ml/kg/ ml/kg/ FmO₂ ÷ ml/kg/ min min FiO₂ FmO₂FiO₂ min Vi ÷ VO₂ 5.0 6.0 0.70 −0.80 −1.14 1.0 1.2 5.0 10.0 0.70 0.400.57 5.0 2.0 5.0 20.0 0.70 0.60 0.86 15.0 4.0 5.0 30.0 0.70 0.64 0.9125.0 6.0* 5.0 40.0 0.70 0.67 0.94 35.0 8.0 5.0 50.0 0.70 0.67 0.95 45.010.0 5.0 60.0 0.70 0.68 0.96 55.0 12.0 5.0 70.0 0.70 0.68 0.97 65.0 14.05.0 80.0 0.70 0.68 0.97 75.0 16.0 5.0 90.0 0.70 0.68 0.97 85.0 18.0 5.0100.0 0.70 0.68 0.98 95.0 20.0 5.0 200.0 0.70 0.69 0.99 195.0 40.0 5.0500.0 0.70 0.70 1.00 495.0 100.0 5.0 1000.0 0.70 0.70 1.00 995.0 200.0

[0056] TABLE 7 VO₂ VI K ml/kg/ ml/kg/ FmO₂ ÷ ml/kg/ min min FiO₂ FmO₂FiO₂ min Vi ÷ VO₂ 5.0 6.0 0.80 −0.20 −0.25 1.0 1.2 5.0 10.0 0.80 0.600.75 5.0 2.0 5.0 20.0 0.80 0.73 0.92 15.0 4.0* 5.0 30.0 0.80 0.76 0.9525.0 6.0 5.0 40.0 0.80 0.77 0.96 35.0 8.0 5.0 50.0 0.80 0.78 0.97 45.010.0 5.0 60.0 0.80 0.78 0.98 55.0 12.0 5.0 70.0 0.80 0.78 0.98 65.0 14.05.0 80.0 0.80 0.79 0.98 75.0 16.0 5.0 90.0 0.80 0.79 0.99 85.0 18.0 5.0100.0 0.80 0.79 0.99 95.0 20.0 5.0 200.0 0.80 0.79 0.99 195.0 40.0 5.0500.0 0.80 0.80 1.00 495.0 100.0 5.0 1000.0 0.80 0.80 1.00 995.0 200.0

[0057] TABLE 8 VO₂ VI K ml/kg/ ml/kg/ FmO₂ ÷ ml/kg/ min min FiO₂ FmO₂FiO₂ min Vi ÷ VO₂ 5.0 6.0 0.90 0.40 0.44 1.0 1.2 5.0 10.0 0.90 0.80 0.895.0 2.0 5.0 20.0 0.90 0.87 0.96 15.0 4.0* 5.0 30.0 0.90 0.88 0.98 25.06.0 5.0 40.0 0.90 0.89 0.98 35.0 8.0 5.0 50.0 0.90 0.89 0.99 45.0 10.05.0 60.0 0.90 0.89 0.99 55.0 12.0 5.0 70.0 0.90 0.89 0.99 65.0 14.0 5.080.0 0.90 0.89 0.99 75.0 16.0 5.0 90.0 0.90 0.89 0.99 85.0 18.0 5.0100.0 0.90 0.89 0.99 95.0 20.0 5.0 200.0 0.90 0.90 1.00 195.0 40.0 5.0500.0 0.90 0.90 1.00 495.0 100.0 5.0 1000.0 0.90 0.90 1.00 995.0 200.0

[0058] TABLE 9 VO₂ VI K ml/kg/ ml/kg/ FmO₂ ÷ ml/kg/ min min FiO₂ FmO₂FiO₂ min Vi ÷ VO₂ 5.0 6.0 1.00 1.00 1.00 1.0 1.2* 5.0 10.0 1.00 1.001.00 5.0 2.0 5.0 20.0 1.00 1.00 1.00 15.0 4.0 5.0 30.0 1.00 1.00 1.0025.0 6.0 5.0 40.0 1.00 1.00 1.00 35.0 8.0 5.0 50.0 1.00 1.00 1.00 45.010.0 5.0 60.0 1.00 1.00 1.00 55.0 12.0 5.0 70.0 1.00 1.00 1.00 65.0 14.05.0 80.0 1.00 1.00 1.00 75.0 16.0 5.0 90.0 1.00 1.00 1.00 85.0 18.0 5.0100.0 1.00 1.00 1.00 95.0 20.0 5.0 200.0 1.00 1.00 1.00 195.0 40.0 5.0500.0 1.00 1.00 1.00 495.0 100.0 5.0 1000.0 0.00 1.00 1.00 995.0 200.0

[0059] TABLE 10 VO₂ VI K ml/kg/ ml/kg/ FmO₂ ÷ ml/kg/ VI ÷ Toler- min minFiO₂ FmO₂ FiO₂ min VO₂ ance 5.0 200.0 0.21 0.19 0.90 195.0 40.0 10% 5.0200.0 0.30 0.28 0.94 195.0 40.0 10% 5.0 80.0 0.40 0.36 0.90 75.0 16.010% 5.0 60.0 0.50 0.45 0.91 55.0 12.0 10% 5.0 40.0 0.60 0.54 0.90 35.08.0 10% 5.0 30.0 0.70 0.64 0.91 25.0 6.0 10% 5.0 20.0 0.80 0.73 0.9215.0 4.0 10% 5.0 20.0 0.90 0.87 0.96 15.0 4.0 10% 5.0 6.0 1.00 1.00 1.001.0 0.83 10%

[0060] Tables 1-9 illustrate the FmO₂ achieved at various inspiratorygas flow rates (VI) assuming an oxygen consumption rate of 5 ml/kg/min.An asterisk in the column labeled VI/VO₂ indicates the minimum flow rateof inspiratory gas needed to achieve an FmO2 that is within 10% of thecorresponding FiO₂. The inspiratory gas corresponding to Table 1 was air(21% oxygen). As seen in Table 1, an inspiratory gas flow rate of 50ml/kg/min results in the fraction of O₂ in the mixed gas (mixture ofinspiratory gas and scrubbed exhaled gas) to be about 0.12. Thus, theratio of FmO₂ to FiO₂ is about 0.58. To achieve the fraction of oxygenin the mixed gas (FmO₂) to be within 10% of the FiO₂, a flow rate ofinspiratory gas of 200 ml/min is needed.

[0061] Tables 2-9 illustrate the flow rate of inspiratory gas requiredfor FiO₂ values of 0.3 (30% oxygen) to 1.0 (pure oxygen). With a higherpercentage of oxygen in the inspiratory gas, a lower flow of inspiratorygas is needed to achieve the same ratio of FmO₂ to FiO₂ For example toachieve an FmO₂ value that is within 10% of FiO2, for gas containing 21%oxygen (air) an inspiratory gas flow rate of 200 ml/min is required,whereas for inspiratory gas containing 80% oxygen, a 10 times lowerinspiratory gas flow rate (20 ml/kg/min) is required (Table 7). Table 10presents a composite of inspiratory gas flow rates for variousconcentrations of oxygen in the inspiratory gas to achieve an FmO₂ valuethat is within 10% of the FiO₂ (10% tolerance level). As seen in Table10, to deliver a desired concentration of oxygen to the patient line 25,one could adjust the inspiratory gas flow keeping the FiO₂ constant, orone could adjust the FiO₂ keeping the inspiratory gas flow rateconstant.

[0062] The data presented in these tables illustrates that by using thedevice of the present invention, inspiratory gas flow rates can bereduced to 6 to 200 ml/kg/min. This compares to an inspiratory gas flowrate of approximately 1000 to 2000 ml/kg/min required with currentlyavailable high frequency oscillatory ventilators.

[0063]FIG. 8 shows steps of a method according to the present invention.In the method, a ventilating device, such as the device 10 describedabove, is provided (step 200). In addition, a patient connected to thepatient line is provided (step 203) and gas is supplied with the gassupply line to the oscillating line (step 206). The oscillator is movedtoward the oscillating line and the outlet valve is opened (step 209).Then, the oscillator is moved away from the oscillating line and theoutlet valve is closed (step 212). Preferably, the gas is supplied tothe oscillating line at approximately a constant flow rate.

[0064] Devices and methods according to the present invention are moreefficient than currently available high frequency oscillatingventilators primarily because the present invention substantiallyreduces the need for bias flow. This reduction in bias flow enablessmaller ventilation systems. It is now clear the device and method ofthe present invention reduces the volume of bias flow required for safeventilation. By using the present device, it is believed the volume ofinspiratory gas delivered to the ventilator can be reduced from 20,000to 80,000 ml/min to as little as 20 to 800 ml/min.

[0065] Another advantage of the present invention may be to counter theloss of mean lung volume associated with prolonged oscillatoryventilation, which is believed to be a problem with this form ofmechanical ventilation. It is currently believed by some that thisproblem might be intensified by reductions in inspiratory gas flow. Oneapproach to this problem that may counter a tendency to lose mean lungvolume and thus preserve lung expansion involves redirection of some orall of the inspiratory gas flow to a small channel adapted to theendotracheal tube to allow delivery of some or all of the bias flowdirectly to the trachea. While potentially hazardous at high(conventional) inspiratory gas flow rates, it is believed that thiswould be safe at the lower inspiratory gas flow rates envisioned forthis invention. Moreover, it is recognized that there might be someadvantage to redirecting some or all of the inspiratory gas flow to thedistal trachea (closer to the lungs) even when practicing oscillationusing conventional high flow rates of inspiratory gas. Redirection ofsome or all of the inspiratory gas to the trachea would trap inspiratorygas in the lung during the inspiratory phase of the cycle, and releaseit to the device 10 at lower pressure during the expiratory phase. Thisshould aid in the expansion of an atelectatic or de-recruited lung.

[0066] Although embodiments of the invention have been described herein,the invention is not limited to such embodiments. The claims whichfollow are directed to the invention, and are intended to furtherdescribe the invention, but are not intended to limit the scope of theinvention.

What is claimed is:
 1. A device for attachment to an oscillatingventilator comprising a gas flow circuit comprising: an oscillating linehaving a first end and a second end, wherein the first end is adaptedfor communication with an oscillator through a connecting tube; apatient line connected to the second end of the oscillating line; areturn line, wherein both ends of the return line are connected to theoscillating line; a check valve in the oscillating line located betweenthe two ends of the return line; and a CO₂ scrubber located in theoscillating line or return line.
 2. The device of claim 1, wherein theCO₂ scrubber is located in the return line.
 3. The device of claim 1,wherein the CO₂ scrubber is located in the oscillating line.
 4. Thedevice of claim 1 wherein the return line has a check valve.
 5. Thedevice of claim 1, wherein the CO₂ scrubber comprises a compoundselected from the group consisting of sodium hydroxide, calciumhydroxide, barium hydroxide and combinations thereof.
 6. The device ofclaim 1, wherein the gas flow circuit further comprises oxygen and CO₂sensors.
 7. The device of claim 1, further comprising a pressure gaugeconnected to the gas flow circuit.
 8. The device of claim 1, furthercomprising a gas supply line connected to the oscillating line or thepatient line.
 9. The device of claim 1 further comprising an outletvalve.
 10. A device for attachment to an oscillating ventilatorcomprising: a) a gas flow circuit comprising: an oscillating line havinga first end and a second end, wherein the first end is adapted forpneumatic communication with an oscillator; a patient line connected tothe second end of the oscillating line; a return line, wherein both endsof the return line are connected to the oscillating line; a check valvein the oscillating line located between the two ends of the return line;a CO₂ scrubber located in the oscillating line or return line. b) a gassupply line in pneumatic communication with the gas flow circuit; and c)an outlet valve in pneumatic communication with the gas flow circuit 11.The device of claim 10, wherein the CO₂ scrubber is located in thereturn line.
 12. The device of claim 10, wherein the CO₂ scrubber islocated in the oscillating line.
 13. The device of claim 10 furthercomprising a bypass line, wherein both ends of the bypass line areconnected to the oscillating line.
 14. The device of claim 13, whereinthe bypass line has a CO₂ scrubber.
 15. The device of claim 10 whereinthe gas supply line is connected to the oscillating line.
 16. The deviceof claim 10, wherein the outlet valve is connected to the oscillatingline.
 17. The device of claim 10 wherein the CO₂ scrubber comprises acompound selected from the group consisting of sodium hydroxide, calciumhydroxide, barium hydroxide and combinations thereof.
 18. The device ofclaim 10, wherein the gas flow circuit further comprises oxygen and CO₂sensors.
 19. The device of claim 10 further comprising a pressure gaugeconnected to the gas flow circuit.
 20. A device for attaching to anoscillating ventilator comprising: a) a gas flow circuit comprising: anoscillating line having a first end and a second end, the first end isadapted for connecting to the oscillating ventilator and having a checkvalve; a patient line connected to the second end of the oscillatingline; and an exhalation line having one end connected to the patientline and the other end connected to the oscillating line and having aCO₂ scrubber; b) a gas supply line in pneumatic communication with thegas flow circuit; and c) an outlet valve in pneumatic communication withthe gas flow circuit.
 21. The gas flow circuit of claim 20 furthercomprising a check valve in the exhalation line.
 22. The device of claim20,wherein the outlet valve is connected to the oscillating line. 23.The device of claim 20 further comprising a recirculation line betweenthe exhalation line and the oscillating line.
 24. The device of claim20, further comprising a bypass line connected to the exhalation line.25. The device of claim 24 wherein the bypass line has a CO₂ scrubber.26. A method of ventilating, comprising the steps of: providing aventilating device having an oscillator, a gas flow circuit comprisingan oscillating line including a first end and a second end, wherein thefirst end is in pneumatic relationship with the oscillator and thesecond end is connected to a patient line, an exhalation line having aCO₂ scrubber and connected to the patient line at one end and to theoscillating line at the other end, and further having a gas supply lineand an outlet valve connected to the gas flow circuit, and a CO₂scrubber; providing a patient connected to the patient line; supplyinggas with the gas supply line to the gas flow circuit; and causing themovement of the oscillator toward and away from the oscillating line.27. The method of claim 26, wherein the gas supplied is a mixture ofoxygen and nitrogen.